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To: "Jan Beulich" <jbeulich@novell.com>
Cc: <mingo@elte.hu>, <tglx@linutronix.de>, <hpa@zytor.com>,
       <markus.t.metzger@intel.com>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] x86: prevent unconditional writes to DebugCtl MSR
References: <47D54185.76E4.0078.0@novell.com>
From: Andi Kleen <andi@firstfloor.org>
Date: 10 Mar 2008 16:56:47 +0100
In-Reply-To: <47D54185.76E4.0078.0@novell.com>
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"Jan Beulich" <jbeulich@novell.com> writes:
>  
> +static inline void update_debugctlmsr(unsigned long debugctlmsr)
> +{
> +#ifndef CONFIG_X86_DEBUGCTLMSR
> +	if (boot_cpu_data.x86 < 6)
> +		return;
> +#endif
> +	wrmsrl(MSR_IA32_DEBUGCTLMSR, debugctlmsr);

It would be better to use checking_wrmsrl() instead of the model
check because often VMs etc. are missing such MSRs too, but 
report the higher family number.

Also silently failing is not very nice, but that's a different issue.

-Andi